Support is requested for the study of regulation of the development of somatostatin-containing neurons in rat retina. A large quantity of somatostatin present early in the embryonic rat retina, with a significant decline in concentration prior to synapse formation, suggesting a role for the peptide in retinal synapse development. The first year of the proposed research will focus on the regulation of somatostatin synthesis at the transcriptional level in an effort to show that synthesis is turned off when somatostatin levels decline. Northern blot hybridization analysis will be utilized to establish the quantity of somatostatin mRNA expressed at key developmental timepoints. Then, in situ hybridization of the somatostatin message will be performed in tissue sections of developing retina to determine that the biosynthesis of somatostatin occurs in defined neuronal populations. To support the hypothesis that somatostatin binding sites will be studied in vitro and autoradiographically. Retinal cell suspensions will then be cultured to define more specifically the molecular mechanisms by which somatostatin is expressed. Firstly, mRNA will be measured and correlated with somatostatin content in this system. Then, the effects of cyclic AMP, which has been shown to regulate somatostatin mRNA accumulation in primary diencephalic cultures, will be monitored. These assays, employing forskolin stimulated activation of adenylate cyclase, will be performed to determine if cyclic AMP regulates somatostatin biosynthesis. Cysteamine, which reversibly depletes somatostatin immunoreactivity and biologic activity in the retina and central nervous system, will be added to tissue cultures to further study the interactions of cAMP activated synthesis in the depleted state. Finally, models of abnormal development including transgenic mice with obligate synthesis of somatostatin, and genetic strain of microophthalmic mice (mi/mi), will be used to study the patterns of somatostatin synthesis and expression in the abnormal state, both in vivo and in vitro.